The present invention relates to apparatus for indicating clipping and near-clipping operation of a signal amplifying transistor operating in an amplifier circuit.
Overdriving of a signal-amplifying transistor results in clipping of signal peaks, thereby distorting the shape of the output signal in relation to that of the input signal. Clipping of audio signals is particularly objectionable to those persons who enjoy true reproduction of sound signals, whether said signals originate in live or recorded form. Very often, the unskilled operator of audio equipment is unaware of the fact that adjustment of a volume control to a higher level does not necessarily increase the volume or power output and that said adjustment often causes clipping which drastically alters the tone quality and the harmonic content of the input signal. In other circumstances, a skilled operator of audio equipment often desires to maximize output power while at the same time minimizing distortion.
Broadcast audio equipment and certain high-quality home audio equipment utilize meters which indicate by moving needle position the instantaneous power of the audio output, thus permitting the operator to adjust the volume to optimize needle peaking and minimize overdriving of output amplifiers. Meters, however, are not generally used on home audio equipment because of the expense and repair associated therewith.
In addition to the aforementioned meters, another method used to indicate overdriving of amplifiers has been through use of incandescent bulbs located on the control panel. However, the intermittent on-off usage of said incandescent bulbs in the particular application causes rapid deterioration of the filaments of said bulbs. Use of light-emitting diodes rather than incandescent bulbs is preferable because of the longer life of said diodes. However, if illumination of light-emitting diodes is limited to instantaneous periods of clipping, the flickering light output resulting therefrom is not sufficiently visible to the equipment operator.